Fix expression evaluation failures on empty scopes (#1998)

Author: Anna Gringauze

Diff for: dwds/CHANGELOG.md

@@ -12,6 +12,7 @@
 - Remove test-only code from `sdk_configuration.dart`.
 - Move shared test-only code to a new `test_common` package.
 - Convert unnecessary async code to sync.
+- Allow empty scopes in expression evaluation in a frame.
 
 **Breaking changes**
 

Diff for: dwds/lib/src/services/expression_evaluator.dart

@@ -143,7 +143,7 @@ class ExpressionEvaluator {
   /// [expression] dart expression to evaluate.
   Future<RemoteObject> evaluateExpressionInFrame(String isolateId,
       int frameIndex, String expression, Map<String, String>? scope) async {
-    if (scope != null) {
+    if (scope != null && scope.isNotEmpty) {
       // TODO(annagrin): Implement scope support.
       // Issue: https://github.com/dart-lang/webdev/issues/1344
       return createError(

Diff for: dwds/test/expression_evaluator_test.dart

@@ -16,6 +16,7 @@ import 'package:dwds/src/services/expression_evaluator.dart';
 import 'package:test/test.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
+import 'fixtures/context.dart';
 import 'fixtures/fakes.dart';
 
 late ExpressionEvaluator? _evaluator;
@@ -94,6 +95,41 @@ void main() async {
                 .having((o) => o.value, 'value', 'true'));
       });
 
+      test('can evaluate expression in frame with null scope', () async {
+        // Verify that we don't get the internal error.
+        // More extensive testing of 'evaluateExpressionInFrame' is done in
+        // evaluation tests for frontend server and build daemon.
+        await expectLater(
+            evaluator.evaluateExpressionInFrame('1', 0, 'true', null),
+            throwsRPCErrorWithMessage(
+                'Cannot evaluate on a call frame when the program is not paused'));
+      });
+
+      test('can evaluate expression in frame with empty scope', () async {
+        // Verify that we don't get the internal error.
+        // More extensive testing of 'evaluateExpressionInFrame' is done in
+        // evaluation tests for frontend server and build daemon.
+        await expectLater(
+            evaluator.evaluateExpressionInFrame('1', 0, 'true', {}),
+            throwsRPCErrorWithMessage(
+                'Cannot evaluate on a call frame when the program is not paused'));
+      });
+
+      test('cannot evaluate expression in frame with non-empty scope',
+          () async {
+        final result = await evaluator
+            .evaluateExpressionInFrame('1', 0, 'true', {'a': '1'});
+        expect(
+            result,
+            const TypeMatcher<RemoteObject>()
+                .having((o) => o.type, 'type', 'InternalError')
+                .having(
+                    (o) => o.value,
+                    'value',
+                    contains(
+                        'Using scope for expression evaluation in frame is not supported')));
+      });
+
       test('returns error if closed', () async {
         evaluator.close();
         final result =

Diff for: dwds/test/fixtures/context.dart

@@ -49,6 +49,11 @@ const isSentinelException = TypeMatcher<SentinelException>();
 final Matcher throwsRPCError = throwsA(isRPCError);
 final Matcher throwsSentinelException = throwsA(isSentinelException);
 
+Matcher isRPCErrorWithMessage(String message) =>
+    isA<RPCError>().having((e) => e.message, 'message', contains(message));
+Matcher throwsRPCErrorWithMessage(String message) =>
+    throwsA(isRPCErrorWithMessage(message));
+
 enum CompilationMode { buildDaemon, frontendServer }
 
 class TestContext {